Confluence will throw a NullPointerException below when it receives a Null value instead of a Group / User name when checking for Group / User permission.

2010-03-24 16:11:01,478 ERROR [http-8080-6] [atlassian.confluence.servlet.ConfluenceServletDispatcher] sendError Could not execute action
 -- url: /pages/getpagepermissions.action | userName: clan | referer: http://localhost:8080/display/permission/Clan%27s+restricted+page
java.lang.NullPointerException
	at com.atlassian.confluence.user.PermittedUserFinder.checkGroupExplicitlyPermitted(PermittedUserFinder.java:51)
	at com.atlassian.confluence.user.PermittedUserFinder.makeResult(PermittedUserFinder.java:43)
	at com.atlassian.confluence.pages.actions.GetPagePermissionsAction.execute(GetPagePermissionsAction.java:84)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:168)
	at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
	at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
	at com.opensymphony.xwork.interceptor.DefaultWorkflowInterceptor.intercept(DefaultWorkflowInterceptor.java:55)
	at com.atlassian.confluence.core.ConfluenceWorkflowInterceptor.intercept(ConfluenceWorkflowInterceptor.java:35)

This can happen when an LDAP group / User was given a permission (eg. view, edit) in Confluence and then was deleted from the LDAP server.

This problem will cause the specific user who created the permission in the first place to not able adding anymore permission to the space.

Clicking on padlock or trying to edit Restrictions will result in the stack trace above in the log file.

No error is visible from the browser.

Workaround

If you hit into this bug and not sure which group to remove from the permission list, the attached patch will help you to identify which groups are causing the problem.

To install:

1. Unzip the zip file into <confluence install>\confluence\WEB-INF\classes\com\atlassian\confluence
   The patch GetPagePermissionsAction.class should reside at <confluence install>\confluence\WEB-INF\classes\com\atlassian\confluence\pages\actions. If you don't have \pages\actions directories under <confluence install>\confluence\WEB-INF\classes\com\atlassian\confluence, create them.
2. Add an extra line in <confluence install>\confluence\WEB-INF\classes\log4j.properties file:

   log4j.logger.com.atlassian.confluence.pages.actions.GetPagePermissionsAction=DEBUG
   

3. Restart Confluence

To use the patch:

1. Visit the problematic page
2. Click on padlock
3. Check <confluence data>/logs/atlassian-confluence.log for something like below:

   010-03-25 11:23:13,212 DEBUG [http-8080-1] [confluence.pages.actions.GetPagePermissionsAction] execute Fetching group object for group name: ldap-group1. Fetched result is: null
   2010-03-25 11:23:13,228 DEBUG [http-8080-1] [confluence.pages.actions.GetPagePermissionsAction] execute Fetching group object for group name: confluence-administrators. Fetched result is: confluence-administrators
   2010-03-25 11:23:13,228 DEBUG [http-8080-1] [confluence.pages.actions.GetPagePermissionsAction] execute Fetching group object for group name: ldap-group2. Fetched result is: ldap-group2
   2010-03-25 11:23:13,228 DEBUG [http-8080-1] [confluence.pages.actions.GetPagePermissionsAction] execute Fetching group object for group name: ldap-group3. Fetched result is: ldap-group3
   2010-03-25 11:23:13,228 DEBUG [http-8080-1] [confluence.pages.actions.GetPagePermissionsAction] execute Fetching group object for group name: ldap-group4. Fetched result is: null
   

In the above there are two LDAP groups that no longer exist (ldap-group1 and ldap-group4) and the Fetched result is null.

For each of the identified groups, please remove by visiting Space Admin > Security > Restricted Pages. Click on the padlock icon for the problematic page, this will take you to a page info view where you can remove individual permissions.

Use the same step above if you want to remove permissions for Null user objects.

The patch will print similar information like above for user names:

2010-04-01 11:32:31,250 DEBUG [http-8080-1] [confluence.pages.actions.GetPagePermissionsAction] execute Fetching user object for user name: clan. Fetched result is: clan
2010-04-01 11:32:31,265 DEBUG [http-8080-1] [confluence.pages.actions.GetPagePermissionsAction] execute Fetching user object for user name: roy. Fetched result is: roy
2010-04-01 11:32:31,265 DEBUG [http-8080-1] [confluence.pages.actions.GetPagePermissionsAction] execute Fetching user object for user name: bambang. Fetched result is: null